1. Field of the Invention
This invention relates generally to device enclosures, and more particularly to manufacturing metallic enclosures for electronic devices. Even more particularly, this invention relates to multi-layered metallic shells and methods of manufacturing such shells.
2. Description of the Background Art
Currently, the demand for electronic devices (e.g., computers, cellular phones, PDA's, etc.) is becoming increasingly more dependent on aesthetics. That is, consumers continuously seek the most up-to-date devices with the latest cosmetically appealing features and differentiating characteristics. As a result, more and more emphasis is being put into the enclosure design of such products. For example, metal enclosures (e.g., housings, battery covers, bezels, etc.) are the current trend in the 3C (computers, communications, and consumer electronics) industry. Devices housed within metal enclosures generally have a more attractive and overall higher quality appearance than that of conventional plastic enclosures.
Conventional metal enclosures typically include a shell and a plurality of mounting features. The shell is often formed from a piece of stamped sheet metal that is most commonly composed of aluminum or some alloy thereof The aluminum sheet metal includes an exterior surface and an interior surface. The exterior surface is typically decorated by one or more surface finishing techniques such as, for example, anodizing, electro-coating, pad/screen printing, dye sublimation, laser marking, etc. The mounting features (e.g., screw bosses, snap-features, etc.) are typically affixed to the interior surface of the shell so as to facilitate the mounting of the enclosure to the host device. In many enclosure designs, the mounting features are formed by some suitable process (e.g. molding) and then attached to the interior surface by some suitable means such as, for example, an adhesive or the like. In other designs, mounting features are formed directly on the interior surface by polymer-to-metal hybrid (PMH) technology which, in general, refers to the various known techniques of bonding polymers to metals. Forming mounting features on aluminum shells by PMH technology typically involves forming tiny pores on the interior surface of the shell and then molding plastic features directly thereon. In forming the pores, the interior surface is typically exposed to some suitable etching agent, for example an acid. The features are molded from a highly viscous plastic that, when in the liquid state, flows into the pores formed on the interior surface. Upon solidification, the plastic hardens to form a mounting feature that is mechanically bonded directly to the porous interior surface of the shell.
Although aluminum and/or aluminum alloy enclosures improve the appearance of products, there are disadvantages. For example, aluminum has a relatively low resistance to plastic deformation and is, therefore, prone to scratch and dent very easily. Of course, scratches and/or deformations on the enclosure substantially degrade the overall cosmetic appeal of the hosting device. Accordingly, the shell is often relatively thick in effort to reduce possible denting and warping of such enclosures.
In effort to alleviate the problems associated with aluminum and aluminum alloy enclosures, some designs incorporate shells formed from different types of metals that are more resistant to plastic deformation. For example, many enclosures are composed of magnesium that formed by some suitable metallurgical process such as, for example, casting. Typically, the shell and mounting features of magnesium enclosures are formed in the same process and from the same material (i.e. magnesium) such that both are one integral part. The magnesium enclosure is typically decorated using some suitable process such as, for example, micro-arc oxidation (MAO), heat transfer, water transfer, painting, etc.
Although magnesium enclosures are less susceptible to plastic deformation than aluminum enclosures, there are still several disadvantages. For example, magnesium enclosures are difficult to produce because of the poor manufacturability of magnesium. As another example, magnesium decorating processes are relatively difficult and, therefore, have a low success rate. As a result, successful throughput is very difficult and, therefore, expensive to achieve in manufacturing magnesium enclosures.
What is needed, therefore, is a design for a metal enclosure that is more resistant to damage. What is also needed is a design for a metal enclosure that can be manufactured with a higher success rate. What is also needed is a design for a metal enclosure that can be decorated with a higher success rate.